bzoj 3676 [Apio2014]回文串
阿新 • • 發佈:2018-12-24
end ble xtend pre new struct spa sin har
這道題在洛谷在洛谷也有(P3649)但數據不好。推薦到bzoj提交
回文自動機的模板題,求出PAM後統計即可。
代碼:
#include<bits/stdc++.h> using namespace std; typedef long long ll; const int maxn = 300000 + 5; struct PAM { int nxt[maxn][26], link[maxn], len[maxn], size[maxn], sz, last; char s[maxn]; void inline extend(int c, int now) { int p = last; while(s[now - len[p] - 1] != s[now]) p = link[p]; if(!nxt[p][c]) { int q = link[p]; while(s[now - len[q] - 1] != s[now]) q = link[q]; link[++sz] = nxt[q][c], nxt[p][c] = sz, len[sz] = len[p] + 2; } last = nxt[p][c]; ++size[last]; } void inline build(char *str) { for(int i = 0; str[i]; ++i) s[i + 1] = str[i]; link[0] = link[1] = 1; len[0] = 0, len[1] = -1; sz = 1; for(int i = 0; str[i]; ++i) extend(s[i + 1] - ‘a‘, i + 1); for(int i = sz; i > 1; --i) size[link[i]] += size[i]; } } pam; char str[maxn]; void inline Solve() { ll ans = 0; pam.build(str); for(int i = 2; i <= pam.sz; ++i) ans = max(ans, (ll)pam.size[i] * pam.len[i]); printf("%lld\n", ans); } int main() { scanf("%s", str); Solve(); return 0; }
bzoj 3676 [Apio2014]回文串